Technical Field
Embodiments of the present invention generally relate to a developer conveyance device and an electrophotographic image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction peripheral (MFP) having at least two of copying, printing, facsimile transmission, plotting, and scanning capabilities, that includes the developer conveyance device.
Description of the Related Art
In electrophotographic image forming apparatuses, it is proposed to use a positive-displacement pump to transport developer that is either toner or a mixture of toner and carrier (hereinafter simply “developer”). Positive-displacement pumps generate pressure by repeatedly varying the volume of an inner space, use the pressure to bring in air or powder from outside on the upstream side, and give discharge energy thereto, thereby discharging the air or powder downstream. Typical positive-displacement pumps include diaphragm pumps, piston pumps, and bellows pumps.
The force for transporting developer (through a conveyance channel such as a pipe) using a positive-displacement pump varies depending on the distance of transportation and the height by which developer is lifted (lifting height). The force increases as the distance and the lifting height increase. Additionally, the strength of force varies depending on the state of developer in the conveyance channel. The force increases as the amount of developer in the conveyance channel increases. The pressure generated by the pump (i.e., capability) is made greater than the force for transport of developer. To increase the capacity of the diaphragm pump, one or more of the size of the pump, the stroke of the diaphragm, the frequency of rotation, and the like are increased. Thus, the device becomes bulkier, and the cost increases.
The following approach is conceivable to maintain the capability to transport developer by the developer conveyance device. For example, developer discharged from the developer container is stored temporarily in a reservoir adjacent to the developer container and stirred by an agitator in the reservoir so that developer contains air and thus fluidized. Then, a pump sucks in and transports the developer. Discharge of developer from the developer container is controlled using a sensor attached to a side wall of the reservoir to keep the amount of developer in the reservoir substantially constant. With this control, the pressure applied to a suction inlet of the reservoir can be substantially constant, and then the amount of developer sucked in by the pump can be constant.